We've cruised Royal Carib, Princess, Norwegian, and Carnival in the past. I would put say that the Zuiderdam was better than Carnival and Norwegian, the same as Royal Caribbean, but not quite as nice as princess. We were a party of 6 with 2 rooms. 8111 and 1035. 3 middle aged adults and 3 in their 20s.
The good: The ports were excellent. Not overcrowded and full days at each port. We didn't do any cruise excursions, instead booking things on our own. Captain Marvins in the Cayman was a highlight and so reasonably priced. The rooms were pretty darned good. Not fancy, but plenty of space, especially in the large inside cabin. It was more spacious than the balcony by far! The bathroom of the balcony room was very good and there was a nice privacy curtain between the sofa bed and big bed in 8111. 3 adults in the balcony room were tight. You couldn't be super tall and still fit on the sofa bed. It would work best for a child. The live music on the ship was fun and plentiful. And you could get a deck chair without committing highway robbery - a nice change. The taco bar and the burger joint were both tasty and easy to use. The game room/library at the very front of the ship was a great place for puzzles, reading, and games. The drinks there were excellent. The Kennedy Center music was outstanding. The singers in BB King Blues club killed it! They were awesome. Public places were clean and they weren't trying to sell you something at every turn. Embarkation and debarkation were a breeze. The National Geographic programming was enjoyed by all ages in my party.
The average: The food. It was only 'OK.' The dining room fare was reasonably bland and portions were small. You could have as much as you wanted. But you had to ask for more of things or multiples. The service was average to good. The buffet was just as good as the dining room. I would skip the dining room altogether next time and opt for the buffets, burger restaurant and taco bar. Daily different ice cream flavors were a treat, though they ran out of cones multiple times. The shows on the main stage were on par with other cruises. Perhaps a bit less heavy on production value, but I'm actually okay with that. Balcony space was sufficient for 2 persons and a small table between. It was fine, but nothing to write home about.
Good balcony cabin. Needs a mattress topper or the pull out sofa isn't usable. Also, we had second room - a large inside stateroom near the theater. It was VERY spacious and more than worth the upgrade from standard inside room. I highly recommend that one. The ship is small enough that unless you have little kids, opt for the larger inside room even if it's not near your second room. It's worth it.